The failure of turbine blades and combustion cans is a substantial hazard to aircraft and power plants. Even when the engine does not fail catastrophically, the breach of a can wall or the loss of a blade tip can produce costly damage. There are few consistent indications of failure because neither the cans nor the turbine blades can be instrumented effectively.
Vibration measurement techniques require that enough of a rotating element be lost to cause a significant imbalance. In most cases this indication shows failure only after propagating damage has already occurred. For the failure of a combustion can, there is little indication in the vibration signature. Burn-through is detected when the fire is consuming much of the engine.
Combustion can burn-through and blade rupture are often preceded by the development of small flaws, intergranular cracking and some crystalline erosion. Combustion gas does not stream evenly past these discontinuities in the surfaces and these spots have inconsistent connectivity to coolant passages. Hot spots are created at these sites. These hot spots are subject to erosion by the combustion gas. The elevated temperature at these sites is also high enough to cause more than the average number of metallic ions to boil off the site.
Similarly, when a weakened turbine blade elongates to rub against the turbine casing, a few particles of the casing or blade tip can be worn away. Once in the combustion stream, the large ratio of surface area to volume makes the particle susceptible to burning and causing additional ion boil-off.
The invention presented monitors the presence of ions of the materials that make up the combustion cans, turbine blades, and turbine casings. These ions are influenced by the earth's magnetic field to radiate an electromagnetic emission whose frequency is a function of the ratio of charge to mass. The emission can be measured with a simple antenna and radio receiver tuned to the extremely low frequency of such emissions. The mass distribution of all ionized particles in the exhaust gas stream is directly related to the spectrum of the emissions.